[FireHeart]

Hello Meg, text or email would be perfectly fine as long as you're sure your friend will see it. All that matters is that you tell him/her. I know it's a very hard thing to do, especially face-to-face. Texting or emailing would be a great idea as you can forward her the article Jenny posted above so that they can understand self harm better and process their initial emotions before seeing you. When you see your friend, if they don't bring it up themselves, you can ask them if they got your email/text and then go from there.
You are a very strong person to be seeking help, it is a very hard, perhaps the hardest, part of recovery for self-harm. Or anything, really. I hope that all goes well and wish you the best of luck. <3